362 H. A. Rowland—Diamagnetic Constants of 
For a circle of rectangular section we must obtain the mean 
value of this quantity throughout the section of the coil. 
ao Lo+7 ptt a 
16 % —$n” po— 4té 
Where &, and p, are the values of x and p at the center of sec- 
tion and 7 and & are the width and depth of the groove in 
which the coil is wound. We can calculate this quantity best 
by the formula of Maxwell (Electricity, Art. 700), 
& rp, , 
M =P, + ae (Ghee + Se) + ete, 
Thus we finally ‘find 
lems: 2 = 1 2 & Ui pay ) 
(2) M= 7 fp A (tres +44,77(Q wt (Se St H) 
+4A,Q'yr"*,+ ete. } 
M’—M’ 
; R 
where R is the resistance of the circuit. If an earth inductor 
1s included in the circuit whose integral area is EH, when it 1s 
reversed the current is — Where H is the component of the 
earth’s magnetism perpendicular to the plane of the inductor. 
The current as measured by the galvanometer in the first case 
M’..} n 
= Csind (1 + 4) 
. , 2H I 2 
ee = Csin gD (144) 
sin¢d 
sing D ; 
«. M’-M" = 2HE 
